Exciton Binding Energies in Wurtzite ZnO/MgZnO Quantum Wells with Spontaneous and Piezoelectric Polarizations

Abstract

The exciton binding energy of ZnO/MgZnO quantum wells (QWs) was investigated by considering spontaneous and piezoelectric polarizations. These results are compared with those of GaN/AlGaN QWs grown on a GaN substrate. With increasing sheet carrier density, both QW structures show that the exciton binding energy is significantly reduced, suggesting that excitons are nearly bleached at typical densities (approximately 10 13 cm 2 ) for which lasing occurs. The exciton binding energy of ZnO/MgZnO QW structures is shown to be much larger than that of GaN/AlGaN QW structures. This can be explained by the fact that ZnO/MgZnO QW structures have a larger matrix element than the GaN/AlGaN QW structures. Also, the self-consistent model of both QW structures shows that, with the inclusion of the internal field, the exciton binding energy is substantially reduced compared to that of the flat-band value.